The Book of Drinks
36/18. Chapter:
It is recommended to lick one's fingers and wipe the bowl, and to eat a piece of food that is dropped after removing any dirt on it. It is disliked to wipe one's hand before licking it, because of the possibility that the blessing of the food may be in that remaining part. The Sunnah is to eat with three fingers
Sahih Muslim
وَحَدَّثَنَاهُ أَبُو كُرَيْبٍ، حَدَّثَنَا ابْنُ نُمَيْرٍ، حَدَّثَنَا هِشَامٌ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ سَعْدٍ، أَنَّحَدَّثَاهُ - أَوْ، أَحَدُهُمَا - عَنْ أَبِيهِ، كَعْبِ بْنِ مَالِكٍ عَنِ النَّبِيِّ صلى الله عليه وسلم بِمِثْلِهِ .
A hadith like this has been reported on the authority of Ka'b b. Malik through another chain of transmitters.
Reference : Sahih Muslim 2032dIn-book reference : Book 36, Hadith 173USC-MSA web (English) reference : Book 23, Hadith 5042